The cleaning process can vary slightly depending upon the condition of the membrane, but the key elements involve a series of chemical applications to remove the foulants and a series of washes and rinses at varying temperature and pH. Even lightly dirty RO Systems should be cleaned once each year to remove small amounts that may form the basis for future build-up of scaling, fouling and/or biofilm problems as months pass.
After the cleaning process the membranes are individually wrapped and ready for shipment to the customer. In addition to cleaning we often manage membrane inventory for our clients so that one set is in operation and one set is cleaned and stored at our facility. We keep a log of all membrane cleanings by membrane serial number and record performance of the individual element. We also test against manufacturer original specifications. We have a wide variety of membranes and housings to fit to your specfic needs
Membrane Cleaning Guidelines - Learn more about GE's Membrane Cleaning Guidelines here. This pdf includes Establishing Baselline Operating Conditions, temperature correction factors, temperature correction factors, temperature correction factors, Recommended Cleaner Circulation and Soaking Times, etc.
Membrane Regeneration - Regeneration service for reverse osmosis (RO) Membranes. RO membrane performance can be negatively impacted by impurities that build up on the membrane surface during operations. Suspended solids, microorganisms and mineral scale can foul membrane elements. These deposits can cause loss in output and/or rejection levels and reduce total system performance. Off-site membrane cleaning and regeneration is quickly replacing typical clean-in-place procedures as a more effective method for removing foulants and restoring membrane performance. Learn more about Regeneration Services.
The cleaning procedure must spell out the sequence. Cleaning usually requires use of a high pH cleaner for organics, silt and biofilm and a low pH cleaner for scale. The common practice is to use the low pH cleaner first, followed by the high pH cleaner, however there are situations where the opposite is the better cleaning strategy.
High pH Precedes Low pH - When fouling occurs by organic and colloidal matter, silt, and/or biofilm the fouling in the membrane cartridge feed passage will block cleaner exposure to scaling. Scaling always occurs at the membrane surface where the concentration of dissolved solids is high. In this situation fouling and scaling are closely interrelated because fouling in the feed passage will diminish the cross flow velocity on the feedwater side of the membrane. This loss of velocity and turbulence will reduce the scrubbing action on the water, and will create slow moving areas of feedwater which will concentrate more than the bulk water, causing scaling to be more prevalent in fouled areas. As scale forms it will bind with the foulant, creating a matrix of the scalant and the foulant, and in severe cases, totally blocking the feed passage and ruining the membrane.
Use of the high pH cleaner first, attacks the organic part of the matrix allowing the cleaning solution to flush away the foulant, opening up the feed passages, and leaving the scale accessible to the next step of low pH cleaning. In some cases, high pH may be the only cleaning step needed.
Fouling from biogrowth creates a tough, gelatinous film formed of the endoskeletons of the bacteria which offers the most difficult challenge to break-up and flush away. Biofilms require the highest of pH cleaning strategies as the first step to break-up, remove, and retard re-growth. As noted above, the biofilm will limit cleaner access to the scaling at the membrane surface.
BIOFILM CAUTION - Exposing biofilms to low pH cleaners as the first step actually makes the film tougher and harder to remove, preventing low pH exposure to scale. The acid cleaners will polymerize the biofilm making the biofilm surface more tenacious. Fouling from hydrocarbons also requires high pH cleaning as the first step. Cleaners with the highest basicity and the highest concentration of surfactants are required to remove the fouling from oils and hydrocarbons.
Low pH is used last – Low pH cleaners effect the membrane polymer and will result in poor salt passage performance for about 24 to 48 hours. If this short term increase in salt passage (permeate conductivity) can not be tolerated, it is best practice to use a high pH, alkaline rinse as the final step after flushing the spent acidic cleaner from the system. The rinse solution should be approximately 8.0 pH concentration. Correct this situation by getting the membrane surface in the 6-8.5 pH range. This can often be accomplished by a 5% concentration of the high pH cleaner strength.
Low pH precedes high pH - When fouling is minimal (very little pressure drop across the housings) and scaling by carbonates or sulfates is the main cause of lost system performance, the cleaning will be more successful if the low pH is used first, or in some cases, the only cleaning step.
Single Cleaning TIP – Using your knowledge of the feedwater and reviewing the cleaning logs from past cleanings, a system that shows only a slight loss of performance may be cleaned satisfactorily with high pH or low pH alone. Choosing a low risk “experimental” CIP using different cleaners save time and money for the plant.
Keep in mind that even lightly dirty RO Systems should be cleaned once each year to remove small amounts that may form the basis for future build-up of scaling, fouling and/or biofilm problems as months pass.
The SDI or silt density index is a measure for the fouling capacity of water in reverse osmosis systems. The test measure the rate at with a 0.45-micrometre filter is plugged when subjected to a constant water pressure of 206.8 kPa (30psi). Did you know that qualitatively, SDI is proportional to particulates and junk going through your membrane elements. A less efficient system costs you money! Save money with ROsave. Patented GE technology on depth filtration media engineered specifically for the highest degree of protection. This product offers low-pressure drop, high particle/dirt capacity which combines to deliver long life and the optimum protection of high performance membrane elements.
Typical Properties of Source Waters
|River||High, with seasonal variation||Moderate||Moderate to High||Low||> 5|
|Lake/Pond||Low, with seasonal variation||High, with seasonal variation||High||Low||> 5|
|Well||Low||Low||Moderate||Low to high||< 5|
|Municipal||Low to moderate||Low||Low to moderate||Low to moderate||> 5 or < 5|
|Brackish||Low||Low||Low to moderate||Moderate to high||> 5|
|Seawater||Low to moderate||Low||Low||High||> 5|
Definition of Characterization
|TDS -ppm||10-150||150-2500||>2500 - Brackish|
|Foulant / Scale||Pretreatment and Cleaning|
|Calcium Carbonate||Control with pH reduction and/or anti-scalant. Easy to clean|
|Calcium Sulfate||Control with anti-scalant. Difficult to clean.|
|Barium Sulfate||Control with anti-scalant. Impossible to clean.|
|Strontium Sulfate||Control with anti-scalant. Difficult to clean. Not Common.|
|Calcium Phosphate||Control with anti-scalant and pH reduction. Easy to clean.|
|Iron||Assuming No Oxidation (Air, CI2). Control with anti-scalant. Easy to clean.|
|Manganese||Assuming No Oxidation (Air, CI2). Control with anti-scalant. Easy to clean.|
|Aluminum||Control with pH reduction and anti-scalant. Easy to clean (not Aluminum Silicate).|
|Silica||Assuming no colloidal silica. Control with anti-scalant. Adjust the pH up or down can help. Impossible to clean.|
|Turbidity||Prefer < 0.2 NTU, 1.0 Max|
|SDI15||Prefer < 3, Up to 5 accepted|
|Iron||< 0.05 ppm|
|Manganese||< 0.05 ppm|
|Aluminum||< 0.1 ppm|
|TOC||< 3 ppm|
|Silica||< 40 ppm|
|pH||TFC (5.0 - 9.0)|
|Temperature||55-85F (12.7 - 30C)|
|LSI||Run anti-scalant program|
|Barium||Run anti-scalant program|
|Strontium||Run anti-scalant program|
|Phosphate||Run anti-scalant program|